The prevalence and incidence of mental ill-health in adults with autism and intellectual disabilities.
Autism alone does not hike mental-ill-health risk in adults with ID—low IQ and Down syndrome explain any gap.
01Research in Context
What this study did
The team tracked the adults who had both autism and intellectual disability. They also tracked the adults with ID but no autism. Both groups had the same IQ range and lived in the same area.
For two years the researchers counted new mental-health diagnoses and checked if problem behavior got better or worse.
What they found
Autism did not raise the odds of anxiety, depression, or psychosis. Both groups had the same number of new cases.
The only difference: adults with autism plus ID took longer to shake severe problem behavior. Recovery was slower by about six months.
How this fits with other research
García-López et al. (2016) looked at teens and saw the same pattern. Youth with autism lagged behind peers with Down syndrome in every sexuality skill. Both studies point to Down syndrome, not autism, as the clearer marker for delay.
McCauley et al. (2018) seems to disagree at first. They found that autistic adults without ID use more anxiety meds and therapy visits. The key gap: their sample had average IQs, while Porter et al. (2008) kept IQ constant and low. Once low IQ is held steady, autism alone adds no extra risk.
Aponte et al. (2025) add the final piece. In autistic adults without ID, anxiety links most to restricted behaviors, not social deficits. Taken together, the three papers show that ability level, not the autism label, drives mental-health load.
Why it matters
Stop assuming every autistic client with ID is doomed to extra mood or anxiety trouble. Screen for Down syndrome and exact IQ instead. Write behavior plans that expect a longer fade-out for severe problem behavior, but keep the same mental-health check-ins you use for any adult with ID.
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02At a glance
03Original abstract
The prevalence, and incidence, of mental ill-health in adults with intellectual disabilities and autism were compared with the whole population with intellectual disabilities, and with controls, matched individually for age, gender, ability-level, and Down syndrome. Although the adults with autism had a higher point prevalence of problem behaviours compared with the whole adult population with intellectual disabilities, compared with individually matched controls there was no difference in prevalence, or incidence of either problem behaviours or other mental ill-health. Adults with autism who had problem behaviours were less likely to recover over a two-year period than were their matched controls. Apparent differences in rates of mental ill-health are accounted for by factors other than autism, including Down syndrome and ability level.
Journal of autism and developmental disorders, 2008 · doi:10.1007/s10803-008-0549-7